stage2: introduce renameTmpIntoCache into the linker API

Doc comments reproduced here:

This function is called by the frontend before flush(). It communicates that
`options.bin_file.emit` directory needs to be renamed from
`[zig-cache]/tmp/[random]` to `[zig-cache]/o/[digest]`.
The frontend would like to simply perform a file system rename, however,
some linker backends care about the file paths of the objects they are linking.
So this function call tells linker backends to rename the paths of object files
to observe the new directory path.
Linker backends which do not have this requirement can fall back to the simple
implementation at the bottom of this function.
This function is only called when CacheMode is `whole`.

This solves stack trace regressions on Windows and macOS because the
linker backends do not observe object file paths until flush().

1 files changed, 48 insertions, 11 deletions

diff --git a/src/link.zig b/src/link.zig
index a720bdada2..5c33ce3b70 100644
--- a/src/link.zig
+++ b/src/link.zig
@@ -636,6 +636,36 @@ pub const File = struct {
         }
     }
 
+    /// This function is called by the frontend before flush(). It communicates that
+    /// `options.bin_file.emit` directory needs to be renamed from
+    /// `[zig-cache]/tmp/[random]` to `[zig-cache]/o/[digest]`.
+    /// The frontend would like to simply perform a file system rename, however,
+    /// some linker backends care about the file paths of the objects they are linking.
+    /// So this function call tells linker backends to rename the paths of object files
+    /// to observe the new directory path.
+    /// Linker backends which do not have this requirement can fall back to the simple
+    /// implementation at the bottom of this function.
+    /// This function is only called when CacheMode is `whole`.
+    pub fn renameTmpIntoCache(
+        base: *File,
+        cache_directory: Compilation.Directory,
+        tmp_dir_sub_path: []const u8,
+        o_sub_path: []const u8,
+    ) !void {
+        // So far, none of the linker backends need to respond to this event, however,
+        // it makes sense that they might want to. So we leave this mechanism here
+        // for now. Once the linker backends get more mature, if it turns out this
+        // is not needed we can refactor this into having the frontend do the rename
+        // directly, and remove this function from link.zig.
+        _ = base;
+        try std.fs.rename(
+            cache_directory.handle,
+            tmp_dir_sub_path,
+            cache_directory.handle,
+            o_sub_path,
+        );
+    }
+
     pub fn linkAsArchive(base: *File, comp: *Compilation) !void {
         const tracy = trace(@src());
         defer tracy.end();
@@ -645,9 +675,11 @@ pub const File = struct {
         const arena = arena_allocator.allocator();
 
         const directory = base.options.emit.?.directory; // Just an alias to make it shorter to type.
+        const full_out_path = try directory.join(arena, &[_][]const u8{base.options.emit.?.sub_path});
+        const full_out_path_z = try arena.dupeZ(u8, full_out_path);
 
-        // If there is no Zig code to compile, then we should skip flushing the output file because it
-        // will not be part of the linker line anyway.
+        // If there is no Zig code to compile, then we should skip flushing the output file
+        // because it will not be part of the linker line anyway.
         const module_obj_path: ?[]const u8 = if (base.options.module) |module| blk: {
             const use_stage1 = build_options.is_stage1 and base.options.use_stage1;
             if (use_stage1) {
@@ -656,20 +688,28 @@ pub const File = struct {
                     .target = base.options.target,
                     .output_mode = .Obj,
                 });
-                const o_directory = module.zig_cache_artifact_directory;
-                const full_obj_path = try o_directory.join(arena, &[_][]const u8{obj_basename});
-                break :blk full_obj_path;
+                switch (base.options.cache_mode) {
+                    .incremental => break :blk try module.zig_cache_artifact_directory.join(
+                        arena,
+                        &[_][]const u8{obj_basename},
+                    ),
+                    .whole => break :blk try fs.path.join(arena, &.{
+                        fs.path.dirname(full_out_path_z).?, obj_basename,
+                    }),
+                }
             }
             if (base.options.object_format == .macho) {
                 try base.cast(MachO).?.flushObject(comp);
             } else {
                 try base.flushModule(comp);
             }
-            const obj_basename = base.intermediary_basename.?;
-            const full_obj_path = try directory.join(arena, &[_][]const u8{obj_basename});
-            break :blk full_obj_path;
+            break :blk try fs.path.join(arena, &.{
+                fs.path.dirname(full_out_path_z).?, base.intermediary_basename.?,
+            });
         } else null;
 
+        log.debug("module_obj_path={s}", .{if (module_obj_path) |s| s else "(null)"});
+
         const compiler_rt_path: ?[]const u8 = if (base.options.include_compiler_rt)
             comp.compiler_rt_obj.?.full_object_path
         else
@@ -742,9 +782,6 @@ pub const File = struct {
             object_files.appendAssumeCapacity(try arena.dupeZ(u8, p));
         }
 
-        const full_out_path = try directory.join(arena, &[_][]const u8{base.options.emit.?.sub_path});
-        const full_out_path_z = try arena.dupeZ(u8, full_out_path);
-
         if (base.options.verbose_link) {
             std.debug.print("ar rcs {s}", .{full_out_path_z});
             for (object_files.items) |arg| {